Internet of Things (M2M, Machine to Machine) refers to that a large number of intelligent terminals are interconnected through a network, thereby implementing collaboration and interoperation. Internet of Things based on cellular radio communications is capable of connecting various intelligent terminals by using an existing cellular radio network, and this is the most economical and effective communication manner at present. With the rapid popularization of M2M application, the number of M2M devices will become huge. These devices combine tightly with wireless communications technologies to obtain data or report data to a control center through wireless connection. A large amount of randomly or periodically reported data is generated, and the data probably comes from various specific applications, such as a wireless water meter and electricity meter, a vending machine, a POS machine, and a remote control device in a smart grid.
An M2M small data service has the feature that a large number of terminals perform transmission simultaneously while the data amount is small. Sometimes, data packets transmitted at a time, such as uplink and downlink periodical heartbeat packets of a large number of users and downlink feedback of RLC/TCP of a large amount of uplink users, are within 10 bytes and even ten-odd bits (bit).
In the existing LTE, a minimum scheduling unit is a resource block (RB, Resource Block) whose size is 144 resource elements (RE, Resource Element) and minimum transmission is 16 bit data. Apart from a control symbol, a channel measurement reference signal (CRS, CSI reference signal) and a demodulation reference signal (DM RS, Demodulation Reference Signal) in the RB, typical configuration is as follows: a normal cyclic shift (CP, Cyclic Prefix), 3 control symbols, 4 transmit antennas, a single stream, and 100 REs used for data transmission. For the data amount of only ten-odd bits and even several bits in the M2M small data service, during transmission of one RB, a symbol rate is 1/10 and even lower, and the spectral efficiency is about 0.14.
It can be seen that resource utilization during transmission of a small data service is quite low and is meaningful only under an extremely low signal to noise ratio. As quality of channel conditions improves, spectral efficiency loss becomes increasingly serious.